1. Field of the Invention
The present invention relates to a power-generation plant provided with a gas turbine that uses low-calorific-value gas, such as blast furnace gas (BFG) or the like, as fuel and to a fuel-gas cooler that cools fuel gas pressurized at a fuel-gas compressor and recirculated.
2. Description of Related Art
There is a known power-generation plant provided with a gas turbine that uses low-calorific-value gas, such as blast furnace gas (BFG) or the like, as fuel and a fuel-gas cooler that cools fuel gas pressurized at a fuel-gas compressor recirculated, for example, as disclosed in Japanese Unexamined Patent Application, Publication No. Hei 9-79046.
In addition, there is a known fuel-gas cooler in which fuel gas is cooled by spraying coolant from a spray nozzle; the coolant, once it has been sprayed from the spray nozzle, used to cool the fuel gas, and then dripped, is recovered with a hopper; and the recovered coolant is recirculated.
However, low-calorific-value gas, such as blast furnace gas (BFG) or the like, contains a large amount of contaminants, and there is a problem in that the contaminants may gradually be deposited at an outlet (bottom portion) of the hopper, thus blocking the outlet of the hopper, and the contaminants may be deposited inside a pipe that guides the coolant accumulated in the hopper to a coolant pit or at an outlet of the pipe, thus blocking the interior of the pipe or the outlet of the pipe. There is also a problem in that, once the outlet of the hopper, the interior of the pipe, or the outlet of the pipe is blocked, it may become impossible to recover the coolant that has been sprayed from the spray nozzle, used to cool the fuel gas, and then dripped, with the hopper alone; the coolant may overflow from the hopper and may flow into a pipe (bypass line) that guides the fuel gas pressurized at the fuel-gas compressor to the fuel-gas cooler or a pipe (extraction line) that extracts the fuel gas from an intermediate stage of the fuel-gas compressor to guide it to the fuel-gas cooler; the coolant may flow into the fuel-gas compressor and the gas turbine when the power-generation plant is stopped; and thus, the fuel-gas compressor and the gas turbine may be damaged.
In addition, in cold regions, etc., in the case in which the power-generation plant is in a stopped state and, in addition, the outdoor temperature falls to 0° C. or below, a coolant pump is operated to spray the coolant from the spray nozzle, thus circulating the coolant in order to prevent the coolant used in the fuel-gas cooler from freezing. However, there is a problem in that, if the coolant is sprayed into the fuel-gas cooler when the power-generation plant is in the stopped state (that is, a state in which high-temperature, high-pressure fuel gas is not supplied (does not flow in)), the interior of the fuel-gas cooler may immediately become over-saturated; droplets may form everywhere in the fuel-gas cooler, thus forming a body of liquid; the liquid may flow into the fuel-gas compressor and the gas turbine by flowing in reverse through the pipe (bypass line) that guides the fuel gas pressurized at the fuel-gas compressor to the fuel-gas cooler or the pipe (extraction line) that extracts the fuel gas from the intermediate stage of the fuel-gas compressor to guide it to the fuel-gas cooler; and thus, the fuel-gas compressor and the gas turbine may be damaged.